1. Field of the Invention
The present invention relates to magnetostrictive materials used for ultrasonic vibration elements, actuators and sensors. The present invention particularly relates to a magnetostrictive material primarily containing iron, a rare earth element, and a transition metal.
2. Description of the Related Art
Alloys RT.sub.2 composed of a specified rare earth element R and a specified transition metal T are known as magnetostrictive materials having a large magnetostrictive constant. Among them, the alloy having a composition Tb.sub.0.26 Dy.sub.0.74 Fe.sub.2 has a large magnetic susceptibility and a large electromechanical coupling coefficient due to low magnetocrystalline anisotropy, and is known as a super-magnetostrictive material having excellent magnetostrictive characteristics. Recently, Tb-Fe-based magnetostrictive materials have also been studied. The materials are produced by annealing quenched amorphous ribbons to form precipitates of fine crystalline phases in order to reduce magnetocrystalline anisotropy.
A magnetostrictive material composed of the Tb.sub.0.26 Dy.sub.0.74 Fe.sub.2 alloy is produced through many production steps as follows. The alloy is melted by high frequency melting or arc melting, the melt is cooled into a given shape, and the product is annealed for a prolonged period to remove process strain. Thus, the process cost is inevitably high.
An effective method for raising the electromechanical coupling coefficient of such a magnetostrictive material is to orient the axis for easy magnetization (hereinafter referred to as the "easy axis") of crystal grains in the texture. Such a means, however, requires high-skill technologies with high production costs. Further, the magnetostrictive material is disadvantageous with respect to workability or processability because of its high mechanical strength and low toughness.
Since the Tb-Fe-based magnetostrictive material including fine crystalline textures is produced as a ribbon, materials having shapes other than a ribbon are obtainable with difficulty.